TypePolicy merge function called before cache deep merge

src/cache/inmemory/__tests__/__snapshots__/writeToStore.ts.snap

@@ -71,6 +71,64 @@ Object {
 }
 `;
 
+exports[`writing to the store root type policy merge is called before cache deep merge 1`] = `
+Array [
+  Array [
+    Object {
+      "existing": Object {
+        "__ref": "Person:123",
+      },
+      "incoming": Object {
+        "__typename": "Person",
+        "age": 28,
+        "id": 123,
+        "name": "Gaston",
+        "status": "ACTIVE",
+        "updatedAt": 100000,
+      },
+      "times": 1,
+    },
+  ],
+  Array [
+    Object {
+      "existing": undefined,
+      "incoming": Object {
+        "__ref": "Person:123",
+      },
+      "times": 2,
+    },
+  ],
+  Array [
+    Object {
+      "existing": Object {
+        "__ref": "Person:123",
+      },
+      "incoming": Object {
+        "__typename": "Person",
+        "id": 123,
+        "status": "DISABLED",
+        "updatedAt": 50,
+      },
+      "times": 3,
+    },
+  ],
+  Array [
+    Object {
+      "existing": Object {
+        "__ref": "Person:123",
+      },
+      "incoming": Object {
+        "__typename": "Person",
+        "id": 123,
+        "status": "PENDING",
+        "updatedAt": 100001,
+      },
+      "times": 4,
+    },
+  ],
+]
+`;
+
 exports[`writing to the store should not keep reference when type of mixed inlined field changes to non-inlined field 1`] = `
 [MockFunction] {
   "calls": Array [

src/cache/inmemory/__tests__/writeToStore.ts

@@ -2496,6 +2496,20 @@ describe('writing to the store', () => {
         },
       },
 
+      {
+        existing:  {
+          __ref: "Account:12345",
+        },
+        incoming:  {
+          __typename: "Account",
+          contact: "[email protected]",
+          id: 12345,
+        },
+        merged:  {
+          __ref: "Account:12345",
+        },
+      },
+
       {
         existing: {
           __typename: "Account",
@@ -2923,6 +2937,157 @@ describe('writing to the store', () => {
     });
   });
 
+  it("root type policy merge is called before cache deep merge", () => {
+    const personMergeMock = jest.fn();
+
+    let times = 0;
+    const cache = new InMemoryCache({
+      typePolicies: {
+        Person: {
+          merge(existing, incoming, tools) {
+            times++;
+
+            personMergeMock({
+              times,
+              existing,
+              incoming,
+            });
+
+            if (tools.isReference(existing) && !tools.isReference(incoming)) {
+              const cachedData = tools.cache.data.lookup(existing.__ref);
+              const existingUpdatedAt = cachedData?.["updatedAt"];
+              const incomingUpdatedAt = incoming?.["updatedAt"];
+              if (
+                typeof existingUpdatedAt === "number" &&
+                typeof incomingUpdatedAt === "number" &&
+                existingUpdatedAt > incomingUpdatedAt
+              ) {
+                return existing;
+              }
+            }
+
+            return tools.mergeObjects(existing, incoming);
+          },
+        },
+      },
+    });
+
+    expect(times).toEqual(0);
+
+    const query = gql`
+      query Person($offset: Int, $limit: Int) {
+        person {
+          id
+          name
+          age
+          status
+          updatedAt
+        }
+      }
+    `
+
+    expect(times).toEqual(0);
+
+    cache.writeQuery({
+      query,
+      data: {
+        person: {
+          __typename: "Person",
+          id: 123,
+          name: "Gaston",
+          age: 28,
+          status: "ACTIVE",
+          updatedAt: 100000,
+        },
+      },
+      variables: {},
+    });
+
+    expect(times).toEqual(2); // TODO: ideally this should only be called once
+
+    expect(cache.extract()).toEqual({
+      ROOT_QUERY: {
+        __typename: "Query",
+        person: {
+          __ref: "Person:123",
+        },
+      },
+      "Person:123": {
+        __typename: "Person",
+        id: 123,
+        name: "Gaston",
+        age: 28,
+        status: "ACTIVE",
+        updatedAt: 100000,
+      },
+    });
+
+    cache.writeQuery({
+      query,
+      data: {
+        person: {
+          __typename: "Person",
+          id: 123,
+          status: "DISABLED",
+          updatedAt: 50,
+        },
+      },
+      variables: {},
+    });
+
+    expect(times).toEqual(3);
+
+    expect(cache.extract()).toEqual({
+      ROOT_QUERY: {
+        __typename: "Query",
+        person: {
+          __ref: "Person:123",
+        },
+      },
+      "Person:123": {
+        __typename: "Person",
+        id: 123,
+        name: "Gaston",
+        age: 28,
+        status: "ACTIVE",
+        updatedAt: 100000,
+      },
+    });
+
+    cache.writeQuery({
+      query,
+      data: {
+        person: {
+          __typename: "Person",
+          id: 123,
+          status: "PENDING",
+          updatedAt: 100001,
+        },
+      },
+      variables: {},
+    });
+
+    expect(personMergeMock.mock.calls).toMatchSnapshot();
+    expect(times).toEqual(4);
+
+    expect(cache.extract()).toEqual({
+      ROOT_QUERY: {
+        __typename: "Query",
+        person: {
+          __ref: "Person:123",
+        },
+      },
+      "Person:123": {
+        __typename: "Person",
+        id: 123,
+        name: "Gaston",
+        age: 28,
+        status: "PENDING",
+        updatedAt: 100001,
+      },
+    });
+  });
+
   describe("StoreWriter", () => {
     const writer = new StoreWriter(new InMemoryCache());
 

src/cache/inmemory/entityStore.ts

@@ -75,7 +75,7 @@ export abstract class EntityStore implements NormalizedCache {
     }
   }
 
-  protected lookup(dataId: string, dependOnExistence?: boolean): StoreObject | undefined {
+  public lookup(dataId: string, dependOnExistence?: boolean): StoreObject | undefined {
     // The has method (above) calls lookup with dependOnExistence = true, so
     // that it can later be invalidated when we add or remove a StoreObject for
     // this dataId. Any consumer who cares about the contents of the StoreObject

src/cache/inmemory/inMemoryCache.ts

@@ -32,7 +32,7 @@ type BroadcastOptions = Pick<
 >
 
 export class InMemoryCache extends ApolloCache<NormalizedCacheObject> {
-  private data: EntityStore;
+  public data: EntityStore;
   private optimisticData: EntityStore;
 
   protected config: InMemoryCacheConfig;

src/cache/inmemory/policies.ts

@@ -226,6 +226,8 @@ export interface FieldFunctionOptions<
   // helper function can be used to merge objects in a way that respects any
   // custom merge functions defined for their fields.
   mergeObjects: MergeObjectsFunction;
+
+  context: ReadMergeModifyContext | undefined;
 }
 
 type MergeObjectsFunction = <T extends StoreObject | Reference>(
@@ -542,7 +544,7 @@ export class Policies {
     });
   }
 
-  private getTypePolicy(typename: string): Policies["typePolicies"][string] {
+  public getTypePolicy(typename: string): Policies["typePolicies"][string] {
     if (!hasOwn.call(this.typePolicies, typename)) {
       const policy: Policies["typePolicies"][string] =
         this.typePolicies[typename] = Object.create(null);
@@ -878,7 +880,7 @@ export class Policies {
       // that need to deduplicate child objects and references.
       void 0,
       { typename,
-        fieldName: field.name.value,
+        fieldName: field?.name.value || "ROOT",
         field,
         variables: context.variables },
       context,
@@ -917,6 +919,7 @@ function makeFieldFunctionOptions(
       );
     },
     mergeObjects: makeMergeObjectsFunction(context.store),
+    context
   };
 }
 

src/cache/inmemory/types.ts

@@ -133,7 +133,7 @@ export interface InMemoryCacheConfig extends ApolloReducerConfig {
 }
 
 export interface MergeInfo {
-  field: FieldNode;
+  field: FieldNode | undefined;
   typename: string | undefined;
   merge: FieldMergeFunction;
 };

src/cache/inmemory/writeToStore.ts

@@ -154,7 +154,7 @@ export class StoreWriter {
     context.incomingById.forEach(({ storeObject, mergeTree, fieldNodeSet }, dataId) => {
       const entityRef = makeReference(dataId);
 
-      if (mergeTree && mergeTree.map.size) {
+      if (mergeTree && (mergeTree.map.size || mergeTree.info)) {
         const applied = this.applyMerges(mergeTree, entityRef, storeObject, context);
         if (isReference(applied)) {
           // Assume References returned by applyMerges have already been merged
@@ -421,6 +421,21 @@ export class StoreWriter {
         previous.mergeTree = mergeMergeTrees(previous.mergeTree, mergeTree);
         fieldNodeSet.forEach(field => previous.fieldNodeSet.add(field));
       } else {
+        // Add the policy type's merge function for individual upcoming payloads
+        if(typename && mergeTreeIsEmpty(mergeTree)) {
+          const typePolicy = policies.getTypePolicy(
+            typename,
+          );
+          const merge = typePolicy.merge;
+          if (merge) {
+            mergeTree.info = {
+              field: undefined as any,
+              typename,
+              merge,
+            };
+          }
+        }
+
         context.incomingById.set(dataId, {
           storeObject: incoming,
           // Save a reference to mergeTree only if it is not empty, because
@@ -660,6 +675,9 @@ export class StoreWriter {
     }
 
     if (mergeTree.info) {
+      if(isReference(existing) && isReference(incoming)){
+        return incoming;
+      }
       return this.cache.policies.runMergeFunction(
         existing,
         incoming,

src/utilities/policies/__tests__/relayStylePagination.test.ts

@@ -130,6 +130,7 @@ describe('relayStylePagination', () => {
       readField: () => undefined,
       canRead: () => false,
       mergeObjects: (existing, _incoming) => existing,
+      context: undefined,
     };
 
     it('should maintain endCursor and startCursor with empty edges', () => {